Evaporator comprising stacked, flat u-shaped tubes

ABSTRACT

The invention relates to an evaporator for exchanging heat between an airflow and a coolant, comprising an array consisting of a single row of flat tubes ( 1 ) stacked in alteration with wavy dividers ( 2 ). Said dividers keep the tubes a distance (d) away from each other, their waves defining the channels for the airflow in the direction of the breadth of the tubes. Each tube has a U-shape, with the ends of each of the two limbs communicating with two chambers of a single fluid container respectively, in such a way as to define a path for the coolant in an even number of segments in the evaporator. According to the invention, the dimension (l) of the evaporator in said direction is between 20 and 48 mm and the distance (d) is between 4.0 and 7.6 mm.

[0001] The invention relates to an evaporator for the exchange of heat between an airflow and a refrigerant fluid with the latter passing from the liquid state to the gaseous state, especially for air-conditioning the passenger compartment of a motor vehicle, comprising a tube bank consisting of a single row of flat tubes stacked alternately with corrugated spacers holding the tubes spaced apart from one another by a distance d and the corrugations of which define passages for the air-flow in the direction of the width of the tubes, each tube having a U-shaped configuration and the ends of its two branches communicating respectively with two chambers of a single fluid box, in such a way as to define a journey in an odd number of passes for the refrigerant fluid in the evaporator.

[0002] Such an evaporator is said to be a “U-circuitry” type evaporator, as opposed to an evaporator with “frontal circuitry” in which each tube defines an individual straight-line journey for the refrigerant fluid between two fluid boxes situated at opposite ends to one another with respect to the tube bank. The number of passes is the number of individual journeys traveled successively by the refrigerant fluid, each along one branch of a tube between the inlet and the outlet of the evaporator. This number is necessarily an even number. Depending on the technology used, the fluid boxes may be affixed, that is to say assembled to the tubes, or not affixed, that is to say formed from the same pieces as the tubes.

[0003] The U-circuitry exhibits the advantage, by comparison with the frontal circuitry, of making it possible to compensate the regions where the thermal exchanges are weak (in particular the area of overheating close to the outlet of he refrigerant fluid) by areas where the exchanges are stronger, thus limiting the thermal imbalance in the airflow leaving the evaporator and enhancing the uniformity of the thermal comfort in the vehicle.

[0004] The U-shaped circuitry also makes it possible, for a given overall size of the evaporator, to have available a larger volume for the passage of the air through the tube bank, thus increasing the exchanges and reducing the loss of pressure head, by virtue of the presence of only one fluid box.

[0005] The object of the invention is to propose dimensional characteristics which are suitable for optimizing the performance of this type of evaporator, more particularly when the number of passes is 4 or 6.

[0006] The invention especially envisages an evaporator of the type defined in the introduction, and provides for its dimension l in the said direction to lie between 20 and 48 mm and for the distance d to lie between 4.0 and 7.6 mm.

[0007] The proposed dimension in the direction of the airflow ensures a reduced bulk of the evaporator in this direction, and a saving of material. It tends, however, to reduce the surface area for exchange between the two fluids. This tendency is compensated for by the choice of a distance d which is also reduced. The combination of these two dimensional characteristics makes it possible to reconcile the reduction in bulk and the saving in material which are mentioned above with a level of performance comparable to that of the evaporators usually used for air-conditioning the passenger compartment of motor vehicles.

[0008] Optional characteristics of the invention, which are complementary or alternative, are set out below:

[0009] the total thickness of a tube lies between 1.0 and 2.7 mm.

[0010] the wall thickness of a tube lies between 0.2 and 0.45 mm, and between 0.2 and 0.7 mm in the case of the nose of the tube.

[0011] the internal thickness of a tube lies between 0.6 and 1.8 mm.

[0012] the half-period of corrugation of the spacers lies between 1.0 and 1.8 mm.

[0013] the wall thickness of the spacers lies between 0.05 and 0.1 mm.

[0014] the tubes and the fluid box are in the form of a stack of pouches each formed from two sheet-metal plates stamped into cup shapes, the concavities of which are turned towards one another and which are brazed together so as to be leaktight at their periphery, each pouch defining one of the said tubes and featuring, at one of its ends, an increased thickness so as to define a segment of the fluid box.

[0015] the fluid box is an independent component featuring apertures through which penetrate the ends of the branches of the tubes, the said ends being brazed so as to be leaktight to the edge of the apertures.

[0016] each tube is formed from two stamped sheet-metal plates which are brazed together, along their lateral edges for the leaktightness of the tube as regards the outside, along a central strip for the separation of the two branches, and at intermediate regions projecting towards the inside of the tube for stiffening it.

[0017] each tube is formed from two stamped sheet-metal plates which are brazed together, along their lateral edges, for the leaktightness of the tube as regards the outside, and along a central strip for the separation of the two branches, the tube being stiffened by an insert brazed onto the inner faces of the plates.

[0018] the tubes are extruded tubes, the end of which opposite the fluid box is blocked off by a cap.

[0019] the tubes are formed from folded pieces of sheet metal, closed by longitudinal brazed Points and blocked off at the end opposite the fluid box, a longitudinal partition being formed by folding or by stamping for separating of the two branches.

[0020] the fluid box comprises two separate, juxtaposed parts, the internal volumes of which communicate respectively with the ends of the two branches of each tube, at least one of the said parts being formed from two elements delimiting the said internal volume, one of which features the said apertures, and, if necessary, from at least one affixed internal partition separating the said internal volume into different chambers each communicating with a subset of the tubes.

[0021] the fluid box is formed from two elements delimiting an internal volume, one of which features the said apertures, and from at least one affixed internal partition separating the said internal volume into at least two chambers, the ends of the two branches of each tube communicating respectively with the said two chambers.

[0022] The characteristics and advantages of the invention will be set out in more detail in the description below, by referring to the attached drawings.

[0023]FIGS. 1 and 2 are partial sectional views of an evaporator.

[0024] FIGS. 3 to 7 are graphs showing the influence of the dimensional characteristics on the functioning of an evaporator.

[0025]FIGS. 8 and 9 are views an longitudinal section of different embodiments of an evaporator.

[0026]FIG. 1 is a partial view in section of the tube bank of an evaporator of the type to which the invention is applied, showing two adjacent flat tubes 1, in transverse section, and the corrugated spacer 2 interposed between them. A few of the dimensions which the invention aims to optimize are indicated here, namely the width l of the tubes, that is to say the dimension of the evaporator in the direction of flow of the airflow, represented by the arrow F1, the distance d between the tubes, fixed by the corrugations of the spacer, the total thickness E_(e) of a tube, that is to say its size in the direction of the stack of the tube bank, the wall thickness e₁ of a tube, and the internal thickness E₁ of a tube, equal to E_(e)−2e₁.

[0027]FIG. 2 is a partial side view of a spacer 2, showing its corrugated profile substantially in sinusoidal shape. The distance d between the two planes P containing the corrugation crests is seen again here.

[0028] The wall thickness e₂ of the spacer, and its corrugation half-period p/2, are also seen.

[0029] According to the invention, the abovementioned dimensions ideally lie in the intervals as below: 20 mm ≦ 1 ≦48 mm 4.0 mm ≦ d ≦7.6 mm 1.0 mm ≦ E _(e) ≦2.7 mm 0.2 mm ≦ e ₁ ≦0.7 mm 0.6 mm ≦ E ₁ ≦1.8 mm 1.0 mm ≦ p/2 ≦1.8 mm 0.05 mm ≦ e ₂ ≦0.1 mm.

[0030]FIG. 3 shows the variation in the heat-exchange capacity of an evaporator envisaged by the invention as a function of the distance d, all other things being equal, and keeping the air throughput constant. It is seen that the maximum effectiveness under these conditions is reached for a value of 4 mm. However, a reduction in the distance d increases the loss of pressure head of the airflow and consequently reduces the air throughput for a given speed of the blower. This is why the values chosen are at least equal to this apparent optimum, that is to say that they lie between 4.0 and 7.6 mm.

[0031] The wall thickness e₁ is chosen so as to ensure an appropriate resistance to pressure and to corrosion, without excessive consumption of material.

[0032] The graph of FIG. 4 shows the variation in the heat-exchange capacity of an evaporator as a function of the internal thickness e₁ of the tubes. When this thickness is low, this results in a loss of pressure head of the refrigerant fluid and a rise in its temperature, impairing the thermal exchange. In contrast, a substantial thickness has the effect of a low speed of the fluid, limiting the heat exchange with the walls of the tubes. The chosen range provides optimized results.

[0033] The graphs of FIGS. 5 and 6 respectively represent the variation in the thermal-exchange capacity of an evaporator and that of the loss of pressure head which it causes the airflow to undergo, as a function of the half-period p/2 of the spacers, the air through-put being kept constant.

[0034] In FIG. 7, the curve depicted by the symbol ∘ and that depicted by the symbol ▾ represent the variation in the loss of pressure head suffered by the air in an air-conditioning apparatus as a whole, as a function of the throughput, respectively for p/2=1.4 mm and p/2=1.7 mm. The curve depicted by the symbol ▪ represents the variation in the back-pressure produced by the blower as a function of the throughput. The intersection of a curve of loss of pressure head and of the curve of back-pressure represents the operating point for the air of the evaporator/blower combination. Thus the air throughput passing through the evaporator is obtained, and the performance delivered by it is deduced therefrom. By repeating the approach for various values of p/2, the optimal value for a given blower is determined. By proceeding thus for various blowers and various air-conditioning casings, the values proposed according to the invention were arrived at.

[0035] The tubes 1 shown in FIG. 1 are each produced by the brazing-together of two plates 1 a and 1 b, stamped so as each to form two marginal longitudinal ribs 1 c and a multiplicity of intermediate longitudinal ribs 1 d. The marginal ribs 1 c of one of the plates are brazed to the marginal ribs of the other plate so as to achieve leaktightness of the tube with respect to the outside. Each intermediate rib 1 d of a plate is brazed to a rib 1 a of the other plate so as to stiffen the tube and to delimit circulation channels 1 e for the fluid within the tube. At the upper end of the tube, some of the channels 1 e communicate with a chamber of the fluid box, and the other charnels with another chamber. The tube is closed at its lower end, and the ribs are interrupted at a certain distance from this end so as to allow the fluid from the descending branch to pass to the ascending branch. The intermediate ribs 1 d can be replaced, wholly or partly, with the exception of a central rib separating the two branches, by stiffening projections of small dimensions not delimiting circulation channels.

[0036] Another means, known in itself, for stiffening the tube consists in inserting into it an insert brazed to the inner faces of the plates, for example a corrugated insert brazed by its corrugation crests.

[0037]FIG. 8 is a partial view in exploded perspective of an embodiment of an evaporator 10 according to the invention, in which the tubes and the two fluid boxes are formed by a multiplicity of pouches 11 which are stacked together from the left to the right of the figure, each consisting of two sheet-metal plates stamped into the shape of cups 12 and 13. The latter are identical to each other and have their concavities turned towards one another, i.e. respectively no the right and to the left. Each cup exhibits a peripheral edge situated in a vertical plane, and the peripheral edges 14 of the two cups forming a pouch are assembled together so as to be leaktight to the fluid by brazing, in order to delimit the internal volume of the pouch. Each cup includes, in its upper part, two juxtaposed regions 15 and 16 with a greater depth than that of the remaining region 17, which occupies the major part of the height of the cup, below the regions 15 and 16. The regions 17 of two associated cups together constitute one tube of the tube bank and feature respective central vertical ribs 18, interrupted above the lower edge 19, in order to separate the two branches of the tube. The regions 15 of the same cups define between them an individual volume forming part of the internal volume of the corresponding pouch and communicating with the upper end of one branch of he tube, each individual volume communicating with the individual volume of at least one adjacent pouch, via apertures 20 formed in the bottom of the cups, so as to form a chamber of the fluid box. Likewise, the regions 16 of the cups define between them individual volumes communicating with the upper ends of the other branches of the tubes, and together form one or more chambers of the fluid box. The corrugated spacers 2 are brazed to the outer faces of the intermediate regions 16 of the cups 11, 12.

[0038]FIG. 9 shows an evaporator 30 including tubes 1 produced independently of the fluid box, for example in the form of extruded tubes, or, in a known way, by folding pieces of sheet metal and forming longitudinal brazed joints. The fluid box 31 comprises a manifold plate 32 featuring a multiplicity of apertures 34 into which penetrate the ends of the branches of the tubes 1 and equipped with a peripheral rim 33 turned upward, that is to say away from the bank of tubes. The upper manifold plate serves as a cover for a tank-shaped piece 34, the peripheral edge 38 of which is brazed to the rim 33, the two pieces delimiting the internal volume of the fluid box, which is divided into at least two chambers by a longitudinal partition. Caps 35 block off the lower ends of the tubes 1 and allow a passage from one pass to the other.

[0039] In a variant, the fluid box can be produced in two juxtaposed parts, the internal volumes of which communicate respectively with the two branches of each tube, each part being formed from a manifold plate similar to the plate 32 and from a tank similar to the tank 34. Depending on the number of passes to be implemented, the internal volume of at least a part of the fluid box, as well as at least one of he sub-volumes delimited by the longitudinal partition o the fluid box 31, can be subdivided by at least one partition into different chambers each communicating with a sub-set of the tubes

[0040] As to the tubes, they can likewise be produced by assembling cups similar to the cups 12, 13 of FIG. 8, but not including the regions 5 and 16 of increased depth. 

1. An evaporator for the exchange of heat between an airflow and a refrigerant fluid with the latter passing from, the liquid state to the gaseous state, especially for air-conditioning the passenger compartment of a motor vehicle, comprising a tube bank consisting of a single row of flat tubes (1) stacked alternately with corrugated spacers (2) holding the tubes spaced apart from one another by a distance d and the corrugations of which define passages or the airflow in the direction of the width of the tubes, each tube having a U-shaped configuration and the ends of its two branches communicating respectively with two chambers of a single fluid box, affixed or not affixed, in such a way as to define a journey in an odd number of passes for the refrigerant fluid in the evaporator, wherein its dimension l in the said direction lies between 20 and 48 mm and wherein the distance d lies between 4.0 and 7.6 mm.
 2. The evaporator as claimed in claim 1, wherein the total thickness (E_(e)) of a tube lies between 1.0 and 2.7 mm.
 3. The evaporator as claimed in one of claims 1 and 2, wherein the wall thickness (e₁) of a tube lies between 0.2 and 0.7 mm.
 4. The evaporator as claimed in one of the preceding claims, wherein the internal thickness (E₁) of a tube lies between 0.6 and 1.8 mm.
 5. The evaporator as claimed in one of the preceding claims, wherein the corrugation half-period ( p/2) of the spacers lies between 1.0 and 1.8 mm.
 6. The evaporator as claimed in one of the preceding claims, wherein the wall thickness (e₂) of the spacers lies between 0.05 and 0.1 mm.
 7. The evaporator (10) as claimed on one of the preceding claims, wherein the tubes and the fluid box are n the form of a stack of pouches (11) each formed from two sheet-metal plates (12, 13) stamped into the shape of cups, the concavities of which are turned towards one another and which are brazed together so as to be leaktight at their periphery, each pouch defining one of the said tubes and featuring, at one of its ends, an increased thickness so as to define a segment of the fluid box.
 8. The evaporator (30) as claimed in one of claims 1 to 6, wherein the fluid box s an independent component (31, 32) featuring apertures through which penetrate the ends of the branches of the tubes (1), the said ends being brazed so as to be leaktight to the edge of the apertures.
 9. The evaporator as claimed in claim 8, wherein each tube is formed from two stamped sheet-metal places (1 a, 1 b) which are brazed together, along their lateral edges (1 c) for leaktightness of the tube with respect to the outside, along a central strip for the separation of the two branches, and in intermediate regions (1 d) projecting towards the inside of the tube for stiffening it.
 10. The evaporator as claimed in claim 8, wherein each tube is formed from two stamped sheet-metal plates which are brazed together, along their lateral edges for the leaktightness of the tube as regards the outside and alone a central strip for the separation of the two branches, the tube being stiffened by an insert brazed onto the inner faces of the plates.
 11. The evaporator as claimed in claim 8, wherein the tubes are extruded tubes the end of which opposite the fluid box is blocked off by a cap (35).
 12. The evaporator as claimed in claim 8, wherein the tubes are formed from pieces of sheet metal, which are folded and closed by longitudinal brazed joints and blocked off at the end opposite the fluid box, a longitudinal partition being formed by folding or by stamping for the separation of the two branches.
 13. The evaporator as claimed in one of claims 8 to 12, wherein the fluid box comprises two separate, juxtaposed parts the internal volumes of which communicate respectively with the ends of the two branches of each tube, at least one of the said parts being formed from two elements delimiting the said internal volume, one of which features the said apertures, and, if necessary, from at least one affixed internal partition separating the said internal volume into different chambers each communicating with a subset of the tubes.
 14. The evaporator (30) as claimed in one of claims 8 to 12, wherein the fluid box (31) is formed from two elements (33, 34) delimiting an internal volume, one of which (33) features the said apertures, and from at least one affixed internal partition separating the said internal volume into at least two chambers, the ends of the two branches of each tube communicating respectively with two of the said chambers.
 15. The evaporator as claimed in one of the preceding claims, in which the number of passes is chosen between 4 and
 6. 